1. Field of the Invention
The subject matter of this invention relates generally to electrical interconnection apparatus and more particularly to apparatus for flexibly interconnecting a movable circular stem with a relatively stationary terminal.
2. Description of the Prior Art
Circuit breaker apparatus in general and vacuum circuit interrupter apparatus in particular is useful for controlling and protecting electrical systems, apparatus and networks. Circuit breaker apparatus and in particular vacuum circuit interrupter apparatus include separable main contacts disposed within an insulating housing. Generally one of the contacts is fixed relative to both the housing and to an external electrical conductor which is interconnected with the circuit to be controlled by the circuit interrupter. On the other hand, the other separable main contact is movable. In the case of vacuum circuit interrupter apparatus the movable contact assembly usually comprises a stem of circular cross section having the contact at one end thereof enclosed within the vacuum chamber and a driving mechanism at the other end thereof external to the vacuum chamber. A flexible gas-tight bellows separates the vacuum chamber from the external region. The bellow expands and contracts with the movement of the stem so as to allow stem movement while at the same time retaining the integrity of the vacuum. It has been found that the circular shape of the stem is desirable for interconnection with the bellows among other things. Often the electrical interconnection between the aforementioned external apparatus or circuit to be protected by the circuit interrupter and the movable contact is made on the circular stem. It can be seen therefore that a need arises for channeling significant amounts of electrical current from a movable stem to a stationary electrical terminal or contact. One of the most popular ways to accomplish this in the prior art is to utilize a flexible conductor such as braided copper wire or the like. Examples of this may be found in U.S. Pat. No. 3,941,959 entitled "Vacuum Switching Apparatus With a Drive Unit and Ground Potential" issued Mar. 2, 1976 to Kohler et al. Another example can be found in U.S. Pat. No. 4,091,251 entitled "Vacuum Switch" issued May 23, 1978 to Amsler. Another way of tapping electrical current off a movable stem is with the aid of a sliding contact such as is described in U.S. Pat. No. 4,025,886 entitled "Electrical Circuit Breaker With Electro-Magnetically-Assisted Closing Means" issued May 24, 1977 to Barkan et al. All of the aforementioned have certain problems relative to known electrical and mechanical properties of conductors. Of particular importance are the electrical characteristic of contact resistance, the mechanical characteristic of flexibility and the general characteristic of construction cost and simplicity and their interrelationship. For example, with respect to the electrical characteristic of contact resistance it has been found that when a single electrical conductor is fastened to another electrical conductor, electrical contact is made in only three relatively small regions between the two conductors. This is regardless of the size of the common surface area of the conductors. This means that a relatively large conductor with a relatively large and inflexible surface area interconnected with another relatively large conductor and bolted in many placed thereto would still only make effective electrical contact at three regions in the contiguous surface therebetween. If on the other hand, one of the large conductors was divided into a number of independent and more flexible small conductors having the same effective surface area and were bolted independently to the other conductor each of the small conductors would now have three of its own regions of contact although the total contact resistance may not increase. However, in a case such as that the complexity and cost of the construction process would increase because multiple conductors would have to be interconnected with one conductor rather than a single conductor being interconnected with a single conductor. It would be advantageous therefore if a contact arrangement between the movable stem of a vacuum circuit interrupter, for example, and a fixed electrical terminal could be made with a flexible interconnection having multiple independent contact surfaces. With regard to flexible braided copper wires, for example, it is obvious that the flexibility is great but the relative complexity and cost of separating the braided wires into multiple separate interconnections with the movable stem increases. The problems associated with flexibility and multiple three point contact areas is exemplified in previously referred to U.S. Pat. No. 3,941,959 where a single massive interconnecting block is attached to a movable stem. The size, weight, and current carrying capabilities of the block seems to be great. However, it is to be remembered that only one three point contact arrangement is made. It would be advantageous therefore to provide apparatus for removing current from a movable circular stem to a fixed terminal by way of a flexible conductor where multiple three point electrical contact regions are established, where the manufacturing process for installation is relatively simple and where the flexible conductors are nevertheless stiff enough to prevent inadvertent contact with each other or with other apparatus in the vicinity of the circuit interrupter so that the use of insulation on the flexible electrical conductor can be avoided to thus retain flexibility and also provide enhanced heat dissipation characteristics.